Abstract: This is an apparatus for measuring the intensity of a seismic shock applied to the apparatus. The apparatus includes an enclosure in which is a system of weights movable in response to an applied mechanical shock, and connected to a movable transmission member. The transmission member contacts a first spiral cam rotatably mounted on a balanced rockable lever. The cam turns the lever angularly when the transmission member is moved by the weights. A spring connected to the lever tends to inhibit it from turning out of its balanced position when the transmission member moves. A second spiral cam is also rotatably mounted on the lever. A fixed stop member contacts the second cam to prevent the lever from turning back to its original balanced position when the lever is turned out of this position in response to an applied mechanical shock. An index needle connected to the lever indicates on a scale the amount that the lever has turned.